The present invention relates to a full or partial tunnel wedge positioned in a propeller shaft tunnel aft of the propeller on a waterborne craft which increases water pressure aft of the propeller and reduces the shaft horsepower required to maintain a given speed.
Existing propeller shaft technology does not allow the water aft of the propeller to converge. Prior art shaft tunnels include those disclosed by Stuart, U.S. Pat. No. 3,515,087, U.S. Pat. No. 3,626,894, and U.S. Pat. No. 3,937,173. In all of the Stuart patents the propeller shaft tunnel is flared out aft of the propeller so as to meet the stern transom and allow the water flow to diverge.
Additional prior art shaft tunnels are disclosed in Munro, U.S. Pat. No. 2,812,738, and Wollard, U.S. Pat. No. 3,469,557. Both Munro and Wollard disclose shaft tunnels wherein the top of the channel aft of the propeller slopes downward. Neither Munro nor Wollard disclose a shaft tunnel which converges aft of the propeller so as to increase propeller thrust and reduce the hull drag of the shaft tunnel.